Technical Bulletin Issue 13 by Sava

SAVA Technical Bulletin For registered members of the SAVA Scheme

Issue 13 | December 2011 All content © National Energy Services, Ltd Welcome to the latest issue of the SAVA Technical Bulletin (formerly HI Technical Bulletin). The bulletin focuses on Home Condition Surveys and associated non-energy issues. We trust that you will find the bulletin useful for your day-to-day work and we welcome any feedback you have about what you would like to see covered in future editions. The contents of this technical bulletin may supersede certain scheme rules or requirements appearing in the Product Rules, Inspection and Reporting Requirements, training manuals or elsewhere. Members must therefore ensure that they have read and understood this document.

IN THIS ISSUE HCS improvements

Practical Land Law for surveyors

Finlock gutter defects

Changes beneath our feet-shared drainage

Services that kill–the CR3 exception?

Using Portland cement to repair traditional lime mortar masonry

HCS improvements We recently sent out a HCS survey and thank you to all of you that completed this. As a result of the survey we have made some changes to the HCS report. These changes are just the beginning of changes we are planning to make over the coming months. HCS changes: 1. Improvement to the layout of photos, i.e. now centralised 2. Removal of the number of habitable rooms (not required with HCS) 3. Extension age text—new boxes will be added when there are multiple extensions and the text ‘the extension was built in’ has been removed 4. Explanation of what SAVA stands for in the ‘About this report’ section

7. Ability to put line breaks in paragraphs (such as general description) 8. Changes to ‘ongoing structural movement’ and ‘trees on clay subsoil’ 9. If there are no dampness issues this is stated on the report rather than being left out if the input box was left blank We have also updated Instruction Manager so your clients now have the ability to instruct you to complete a Home Condition Survey report. We will include a reminder about how to use Instruction Manager in the next Top Tips. We hope you will find these changes useful and should you need any further assistance with NES one, please do not hesitate to contact our Technical Support team on 01908 442105 or email support@nesltd.co.uk

5. New option of ‘triple garage’ 6. B5—the central heating tab has been removed

Page 1 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ©Nati onal Energy Services

Finlock gutter defects– a case study A chance call from a client to ask if we could help explain the cause of a damp patch has provided an interesting and thought provoking example of an alternative cause for a common defect. The client reported that they had a damp patch in their bedroom which became more pronounced after rain. The property was known to be a 1950s or early 1960s detached bungalow of cavity brick and rendered wall construction. The cavities had been insulated around two years ago. The bungalow also had Finlock gutters, which are a less common feature for an individually built bungalow. Finlock precast concrete gutters are a proprietary reinforced concrete combined gutter and cavity closer that became popular in construction in the post war era of the 20th century. They were considered to be generally robust and low-maintenance and consequently were widely used on local authority housing, factories, schools, flats and other buildings with medium and low-pitch roofs. Although used in speculative construction they were not as common as in private sector building construction.

Photo 1: a typical example of Finlock gutters at this classic example of a social housing dwelling.

The Finlock gutter system is formed of concrete interlocking sections (see Photo 1 above). These are laid on the top of the wall at eaves height and perform the multiple functions of:



Providing a closure to the top of cavity masonry inner and outer leaves



Forming a rigid beam at eaves level above, any opening such as windows and doors in the wall is capable of supporting the roof structure above



Providing a concrete trough gutter that can then be lined

The gutter trough was typically lined with bitumen to provide a water-proof membrane and stop penetration through the concrete into the fabric of the building. Upon visiting the property we discovered that the dampness extended from the bottom of the internal surface of the external wall of the bedroom, but was also creeping onto the internal partition wall between the bedroom and the adjacent bedroom (see Photo 2). The dampness was also visible in the built-in wardrobe of the bedroom on the other side of the partition wall, but not to the same extent. Moisture meter readings taken in the wall also indicated that the dampness extended to at least 1.2 m above both internal and external ground levels. This ruled out rising damp or leaks from heating pipes below as a possible cause.

Photo 2: the extent of the damp patch in the bedroom of the bungalow. Note that the wall paper has lifted from the wall surface and there is extensive mould growth.

External inspection of the wall allowed identification of the cause of the dampness, i.e. the Finlock gutter must be leaking. Deterioration of the original linings over time (see Photo 3), in particular the seals between individual Finlock units due to differential movement and expansion (see Photo 4), has meant inevitable failure.

The presence of mould indicated that the source of the dampness was most likely to be pure water. Water containing salts is more typically associated with either rising damp, where the earth salts are carried in solution in the rising moisture, or from salt contamination of the building materials that are associated with both rising and penetrating damp. The mould would therefore indicate that this was dampness caused by some form of leak from above or below or alternatively (but less likely) a condensation issue. Curiously, neither in the wardrobe on the other side of the wall, nor in the room where the damp patch was most visible, was there any indication of mould growth at the top of the internal surface of the external wall (see Finlock gutters and condensation—cold bridging on page 3). The typical defects related to condensation and Finlock gutters could therefore quickly be eliminated.

(Continued on page 3)

Photo 3 above: examination of the bungalow’s gutters indicated that the bitumen lining to the Finlock gutter has deteriorated. Photo 4 left: crack in the joint between sections of the Finlock concrete gutter, as seen on the underside of the gutter.

Page 2 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ©Nati onal Energy Services This resulted in leaks which can affect both the external wall and the cavity itself. This is a problem that eventually manifests as damage and dampness to the internal wall. The example of this property is a particularly bad case where the failure of a single joint between concrete sections allowed water to penetrate and run down into the cavity of the wall below. The introduction of retro-fit insulation in this particular case had allowed dampness to develop extensively through the internal wall surface (see Photo 2). In addition, the water soaked through the external masonry leaf, dripping from the back of the render and materialising as a further damp patch on the surface of the external bricks below the render (see Photo 5).

There are four possible solutions to the issues associated with leaking Finlock gutters: Removal and ‘replacement’: the concrete gutter trough is cut away from the wall to leave the cavity closer part of the Finlock in situ. A new facia is secured over the cut concrete and a gutter mounted onto the facia board. Replacement can disguise the presence of the original gutters and is something to be conscious of when you encounter condensation at upper wall level of the internal surface of main walls (see Finlock gutters and condensation—cold bridging). Always look at adjacent properties to identify the possible presence of cut Finlock gutters. Lining with bitumen or felt: this is one of the earliest solutions to leaking concrete gutters and will only lead to the same problems developing at a later date. Lining with metal alloys: extruded aluminium and zinc have been used as liners to the concrete troughs with some success. However, issues with thermal expansion of the materials and in trying to form water proof joints may lead to the eventual need to replace the liners.

Photo 5 : note the damp patch to the external surface of the wall which is corresponding to the dampness also visible to the internal surface of the same wall in Photo 2.

During and after rain showers water can be visibly seen to drip from the bottom of the render. Obviously we do not make recommendations for repair by way of further advice in the Home Condition Survey but this was a specific defect inspection and knowledge of the forms of repair is vital in understanding Finlock gutters and their defects. This will allow us to determine the condition rating for such defects and it is therefore appropriate that we consider these here.

Lining with resin based materials: resin based liners have become the most recent solution to the problem of leaking Finlock gutters. The materials and application process are similar to the coverings used on flat roofs etc, whereby a fibre matting layer is laid in the trough and the resin is mixed and poured into the trough of the gutter to form a continuous liner without joints. This has several advantages over the other lining methods in that:

Two other issues to be aware of relating to Finlock gutters Structural failure One of the strengths of Finlock gutters is that they form a relatively strong beam capable of providing lintel support over openings. However, in some situations the strength of the Finlock system might be assisted by the strength in the window and door frames below. Where the old frames have been replaced with uPVC frames some properties have been affected by excessive downward pressure on the Finlock systems as a consequence of the removal of additional support provided by the frames. This can result in dishing of the gutters over openings as well as distortion in the uPVC frames themselves, indicated by fanlights that are difficult to open or stick. Finlock gutters and condensation— cold bridging One of the most common issues associated with Finlock gutters is the development of condensation in the building. This is caused by the cold bridge that is formed across the cavity by the concrete sections. Finlocks might be good as a cavity closer but the concrete material has a high thermal conductivity thus allowing a cold surface to be present at the upper internal wall surface of rooms where the gutter system is present. This in turn allows condensation to develop quickly where the balance in heating, insulation and ventilation is poor. Ian Brindle Chartered Surveyor

 it is a cold poured process (unlike bitumen) and so there is no associated risk of fire;

 it is without joints and so does not incorporate points of weakness unlike both other forms of lining;

 it is a more reliable long term solution that is also less expensive than the other three forms of repair/ replacement.

Page 3 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ©Nati onal Energy Services

Services that kill–the CR3 exception? The introduction of the revised Condition Rating Protocol (Issue 4) has raised the standard to meet industry developments on the condition rating of services. In the previous issue of the SAVA Technical Bulletin (Issue 12) we discussed arguments relating to services that kill. To recap: where a service installation that is powered by a combustible fuel or an electrical installation has not been tested, this attracts a condition rating of 3, inline with the recommendations of the various government approved accreditation schemes for such industries’ recommendations regarding testing. This is not to say that all defects associated with services that kill justify a CR3. In making the decision, any defect with such services is related to whether the defect constitutes a safety hazard to the installation. There is at least one probable exception that has so far been identified: this is the deficient condensate drain pipe connected to the condensing boiler. During the winter of 2010 several incidents occurred where condensate freezing in the pipes caused the boiler to malfunction. To date the solution to this problem has been either to:

 Retrofit insulation to the

To put this in the context of the protocol, the risk of the pipe freezing and the boiler failing as a consequence is dependent on the weather conditions: starting at A in the condition rating protocol (see over the page) there is a potential hazard and we default to the CR3. At B we then assess the scale of remedy. This remedy is to lag the pipe or replace it; either way the remedy is low scale and therefore we move to box C and assess the scale of risk.

Photo 1: the 22mm diameter condensate pipe running over the top and down the right side of the gas meter cupboard has been lagged with insulation.

For the surveyor, this presents an interesting challenge in determining the condition rating to apply to an uninsulated condensate pipe of the original 22 mm diameter type. This pipe is now considered deficient by surveyors unless insulated. When assessing the condition rating to apply to this issue we must consider the circumstances. The issue is certainly a deficiency if we consider what best practice recommends. However, the issue is primarily a health and safety one as it is the hazard in the pipe freezing and causing the boiler to malfunction that is the perceived risk. The risk from the hazard is potentially greater in winter and less in summer.

In summer the risk of the pipe freezing is less likely but the risk to the boiler might be perceived as quite severe. Therefore using the standard risk assessment method (as illustrated in the diagram below) the risk might be perceived as medium. This equates to a CR 2 according to the protocol. By contrast, in the winter months the risk of the condensate pipe freezing is more likely and the health and safety risk profile from this hazard worsens accordingly. Starting at A in the condition rating protocol there is a potential hazard and we again default to the CR3. At B we then assess the scale of remedy. This remedy is still to lag the pipe or replace it and the remedy is low scale and we therefore move to box C and assess the scale of risk. It should be remembered that this is not an exception to the rule and that if the boiler has not been tested then the installation attracts a CR3.

condensate pipe (Photo 1), or

(Continued on page 5)

 Install a wider (32-40mm) diameter condensate pipe. So far, in both cases the solution has not been fully tested by further winter trial. Some experts are still concerned that further improvement might be required. Also the provision of a wider condensate pipe may have become best practice for installation of new boilers by heating engineers, but Gas Safe and other accreditation schemes are as yet to make the provision of a wider diameter condensate pipe mandatory.

Diagram 1: Health and safety hazard risk assessment grid.

Page 4 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ©Nati onal Energy Services (Continued from page 4) The situation of the potential CR2 in warmer months relates to condensing boilers that have been tested but are noted to have a smaller diameter and an un-insulated condensate pipe. However, it is an interesting example of the need to consider the detail of condition rating assessment and not to apply rules without reflective thought.

There are two courses available where you can learn more about condition rating (as discussed in the article on page 4 of this technical bulletin. A one hour online seminar introduction to the revised condition rating protocol ‘SAVA Condition Rating Protocol’ is now available. For a more detailed look at the application of condition ratings a one day course ‘Applying Consistent Condition Ratings’ is also available. If you would like more details or to sign up to either course please log on to the following link: www.nesltd.co.uk/courses

Page 5 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | © National Energy Services

Practical Land Law for surveyors The first session of our Practical Land Law for Surveyors course, held back in September, stimulated an interesting discussion that proved that there are a couple of issues that need clarification for surveyors writing Home Condition Survey (HCS) reports. The first is the use of the term ‘allocated parking space’ in the HCS. When the report asks how many allocated spaces the property has (as with other reports for valuation and survey), an allocated space is defined where the parking space is separated or ‘off site’ from the main dwelling. There are two typical examples of this:

 The allocated parking space to a flat (edged in turquoise on the plan in Diagram 1), or

 Where the house has a space allocated in a separate communal car parking area, but separate from the house (edged in red on the plan in Diagram 1 below).

The term ‘allocated parking space’ is not an invitation to state how many cars it would be possible to park on the property. The second issue is a legal one and is also covered in the course. Where the owner has made a parking space (or driveway) on site but there is no dropped curb in the pavement to allow access (as illustrated in Photo 1) then there is legally no provision to draw a vehicle off the road onto the property. This point should be made clearly in the HCS report to avoid misleading the client (and a negligence claim). Permission from the Local Authority to drop the curb has to be obtained and a licence to carry out the work at considerable expense. If you would like to attend the Practical Land Law for Surveyors course which covers these and many other issues that should be clearly drawn to the attention of the legal adviser in the HCS, please visit our website at www.nesltd.co.uk/courses.

Photo 1: both semi-detached houses in the photo have car parking spaces created at the front of the properties but neither has a dropped curb which indicates that no consent has been obtained from the Highways Authority to draw a vehicle off the road onto the property.

Photo 1a: detail view of curb from photo above.

Diagram 1: Plan of a development of houses and flats. The house marked in red has an allocated parking space near to the plot. The flat meanwhile marked in turquoise also has an allocated parking space in the communal car park.

Page 6 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ÂŠNati onal Energy Services

Changes beneath our feet Responsibility for the drains beneath our feet has changed significantly. On 1 October 2011 all shared drains within the curtilege of a property became the responsibility of the Water Utilities. Also, by the end of 2011 all discharges from private septic tanks or package treatment plants must be registered. For the surveyor undertaking the HCS this has an impact on what to consider when making enquiries about and inspecting drains. It does not necessarily affect the fundamentals of how you report them in the HCS but there might be some additional commentary needed. This article sets out the changes and considers how we should report on individual situations.

Shared drainage Before 1 October 2011 we as surveyors would have noted the condition of below ground drainage when we lifted the manhole covers, but we would have also identified if any part of the drain was shared with neighbouring property. In the event that it was a shared system we would have highlighted this to the legal adviser in section C. This requirement has not changed. It is estimated that up to half of all properties in England and Wales are connected to, and the owners are responsible for, a private sewer. However, from 1 October drainage pipes that serve more than one property and which are situated within the curtilege of the property have become the responsibility of the Water Utility Company (see Diagram 1). If there is a leak, then the Water Utility Company will be responsible for the repair to the shared pipes. In addition, if there is a problem with the drains, in the first instance it will be the home ownerâ&#x20AC;&#x2122;s responsibility to identify that the leak is from the shared pipe and not from a section of pipe which only serves the subject property. Irrespective of the change it is therefore still important that the surveyor

Diagram 1

identifies if any of the drains are shared and that he draws this to the attention of the legal adviser.

responsibility. Again a note to this effect will flag the issue up to both the legal adviser and your client.

There is an exception to this change, where some properties are connected to a private pumping station before they connect into the main sewer network. It is likely that a home owner will know if they are connected to a private pumping station as they will pay service charges for its maintenance. However, owners of flats and similar situations might not be aware that they pay for a pumping station within their service charge as this will cover a whole range of maintenance etc that they pay for.

How to advise on a property with complex drainage issues therefore needs serious consideration. The following case study outlines one situation where these issues are being considered.

The government plans to transfer the ownership of these pumping stations to Water Companies on 1 October 2016. Until this time, the owner(s) of the pumping station will continue to be responsible for maintenance and repair to the pumping stations. If there is a private pumping station then it is important that this has been registered with the Water Utility Company before the deadline so that they are fully aware of it and take over

Case study of a shared drainage system The property being considered is No. 32 Oakridge Road, illustrated in the series of diagrams (Diagrams 2 to 4 on the following pages). The property has a shared drainage system that runs along the back of the property. The sewage pipe (sections A & B in diagrams 2 to 4) is shared with No. 34 and carries soil and waste to a 2.5 m deep storage chamber (a private pumping station), that is actually situated in the garden of No. 30. The head of this is shown in Photo 1 over the page.

(Continued on page 8)

Page 7 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ÂŠ National Energy Services (Continued from page 7) Photo 2 shows the access into the chamber and the rather old, corroded and broken sump pump which lifts the sewage from the chamber and pumps it through a 50 mm pipe (C) around the house before discharging it into an inspection chamber at the front of the house. A standard clay pipe then carries the outflow from both the adjacent houses and from the subject property to the mains sewer in the road, which is adopted by the Water Utility Company.

Photo 1: the private pumping station, the top of which provides a raised patio area in the garden of No. 30.

Photo 2: inspection access to the chamber and the rather old, corroded and broken sump pump which lifts the sewage from the chamber.

Before October 2011 the surveyor encountering this would have advised that there were shared drains and that the property was not directly connected to the mains sewer. A further complication is that the power for the pump to the pumping station is supplied by No. 32. This in itself would have taken some careful explanation in the drainage section of the HCS. As a consequence of the changes effective from 1 October 2011 the shared drainage (section B) will not be adopted by the Water Utility Company, but section C and everything coloured purple in Diagram 3 from the private pumping station to the main sewer would be adopted. Only from the 1 October 2016 will the Water Utility Company take over responsibility for the drainage including the private pumping station and section B of the drainage pipes (see areas coloured purple in the Diagram 4 over the page).

Diagram 2

The drainage pipe in section A will always remain the responsibility of the land owners but there might be still responsibilities for maintenance to clarify as part of this pipe which only serves No. 34 is on the land of No. 32. This can only be clarified by the legal adviser. Currently, reporting this situation relating to No. 32 in the HCS would require several issues to be identified:

(Continued on page 9) Diagram 3

Page 8 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | © National Energy Services (Continued from page 8) 1. Firstly that there is a drain serving No. 34 only that is partly within the demise of No. 34 and the need to clarify responsibility for future maintenance; 2. There are shared drains (section B) and a private pumping station (with electricity provided at cost to No. 32); 3. The private pumping station connects the two properties No’s. 32 and 34 to the mains sewer. This cannot easily be outlined in Section C and if you cannot do so the only way to advise the client and the legal adviser is to build a reference into Section C and describe the complications in the drainage section of the report. In this particular example the pump is broken and actually inadequate (there should be a back up pump) and so describing the various assumed responsibilities is critical to repair.

Registering discharges from septic tanks and other forms of private drainage Also during recent months there has been a requirement to register with the Environment Agency a discharge of what are known as exempt discharges of sewage effluent from a septic tank or sewage treatment plant. Discharges to rivers or streams should already have been registered and the time is running out for discharges to ground, which should be registered at any time before 1 January 2012. The scale of what is deemed exempt is a daily volume of 2 m3 of sewage effluent to the ground or 5 m3 (pre-treated in a package treatment plant) to surface water. To put this in context it is estimated that an eight bedroom house would produce up to 1.8 m3 of sewage so this covers the majority of properties that we would inspect for the purpose of providing a HCS. Registration is free and, while most householders with a sewage effluent discharge will be able to register, the Environment Agency may not be able to

Diagram 4

accept a registration if it is close to a nature conservation area. The Environment Agency will check for this when a discharge is registered. In such cases they will recommend that there be an application for a discharge permit and in such situations the property owner might already possess one. Photo 3 shows a typical indication that the drainage system is probably not connected to the mains. This line of inspection chamber covers provides access to an old septic tank. The condition of the covers is poor and further investigation could be necessary. Irrespective of this the outflow from this system must be registered with the Environment Agency. The exception to registration is cesspools as they are sealed tanks with no discharge to the environment. Cesspools usually need emptying every few weeks. Even so the surveyor needs to be aware that old cesspools can be an environmental hazard and where there is a risk of leaching into the surrounding ground etc. the issue should be identified for further investigation in the HCS.

Photo 3: a typical indication that the drainage system is probably not connected to the mains.

By contrast, a septic tank is a simple tank that is usually buried in the ground; it has an inflow of sewage from the dwelling and an outflow from the tank. The septic tank allows solid matter to settle in the tank and liquids to flow out. The outflow from the septic tank requires further treatment and this is

(Continued on page 10)

Page 9 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | © National Energy Services (Continued from page 9) normally achieved by soaking it away into the ground (through the ground via a drainage field or infiltration system, also called a soakaway), where bacteria in the soil complete the treatment process. Where the septic tank discharges directly to surface water (a river or stream), it is not possible to register. The property owner should instead have obtained a permit to make the discharge and, if granted, the Environment Agency will normally require the home owner to upgrade to a treatment plant. Often called ‘package’ plants, sewage treatment plants are like mini sewage works and produce much cleaner effluent than septic tanks. For this reason, effluent from package treatment plants can normally be discharged to surface waters. In a very few cases, more relaxed standards may apply where the Environment Agency is satisfied that the discharge will have or is having no detectable impact on the environment (for example, where very high dilution is available in the receiving water body). The Agency will usually allow up to 12 months completing an upgrade, although this depends on individual circumstances. For the surveyor conducting a HCS inspection the identification of a private drainage system has always needed careful consideration. Assuming that the cesspool, septic tank or package plant does not present any issues related to defects, the surveyor must check with the home owner how often maintenance and emptying takes place. The surveyor must also ask where any outflows discharge, consider the surrounding area, and verify with the occupier/owner if the discharge has been registered. A clear description of this needs to be outlined in the HCS with a recommendation that this is confirmed as an addition to the standard legal enquiries.

Using Portland cement to repair traditional lime mortar masonry In the previous edition of the SAVA Technical Bulletin Alan Milstein raised the valid point that older properties should be maintained in the traditional way and walls allowed to function according to the original intension of their form of construction. This article, by Mike Ridgell, picks up the issue of the inappropriate use of cement mortars to repair old masonry walls and explains the science behind why lime is better than cement in preserving the performance of old brick and stone masonry. Surveyors frequently have to decide how to report on the previous use of cement mortar to repair old masonry walls or the application of cement render to such walls. Sometime the effects of such ‘repairs’ are obvious in the form of spalled masonry or in cracked and blown render. Sometimes the pointing or render are relatively new and the potential damage of this deficient repair is not yet apparent. Cement, added over the last seventy years to buildings that should be breathing structures, is at some point going to cause failures, unless remedial work is carried out. Consider the flexibility and strength of a traditional masonry wall. Brick and stone are in most cases highly durable materials which can survive well in most conditions, whether in wet foundations or exposed to the weather. It is now well established that the strength of a brick or stone structure is derived partly from the inherent strengths of the component materials of brick/stone, mortar and their bonding, and partly from friction between the components.

Lime vs. Portland cement Lime mortar was the key ingredient in many walls, used successfully for thousands of years and, in this country, used commonly until the early twentieth

century, although there are many regional and technical variations and exceptions to this. Portland cement, so called because of its visual similarity to grey Portland stone, was patented in 1824. It was supplied in barrels ready for use and must have appeared as an almost magical alternative to conventional lime mortars which required huge amounts of labour to burn and slake the lime in often dangerous conditions. Once slaked, lime was usually left for several months or more to allow it to mature before being used. By contrast, Portland cement was a manufactured material that was comparatively simple to use: mix one part cement with three parts sand, add water and the resulting mortar will be hard by the next day. Compared to the considerable effort and time taken to produce even a simple lime mortar, this alternative must have been most attractive. The rapid set of Portland cement also meant that less time has to elapse before the next few courses of stone or brick can be laid, thus enabling construction to continue more quickly. A hydraulic set is possible, i.e., it hardens under water or in wet situations. Initially, the only restriction to Portland cement replacing lime in masonry wall construction was its cost. In 1850 cement was twice the cost of lime and was therefore predominantly used on important and prestigious structures.

Benefits of lime mortar in traditional construction In terms of long term performance, lime mortars, with both a self-healing capacity and a degree of plasticity and flexibility, have shown themselves to be better suited to the needs of historic buildings than the stronger but more brittle mortars based on Portland cement. In many structures which rest on little or no foundations structural movement is likely, whether seasonal, thermal or of other cause.

(Continued on page 11)

Page 10 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | © National Energy Services (Continued from page 10) Therefore the mortar should be weaker than the stone or brick it surrounds. A soft lime mortar between the masonry allows some movement without noticeable cracking. Cracking, if it does occur, may be fine ‘micro-cracking’. Free lime particles can migrate to these cracks and in some cases effectively repair them. Any ‘damage’ caused by movement in the structure is sustained by the mortar which is sacrificial to the stone or brick, rather than the masonry components. Traditional stone walls (whether rubble or ashlar) and solid brick walls were generally designed to be able to breathe, i.e., to be able to absorb and release moisture and moisture vapour. Rainwater blown against the outside of the wall is absorbed into the outer wall quite readily, perhaps a few millimetres more in wet conditions (see the Diagram 1 on page 12).

Render coating with lime mortar would once have covered many more traditional walls than it now does. After rain, a wet rendered wall dries rapidly by the action of the sun and the wind evaporating away the moisture: as surface moisture evaporates it draws moisture from within the wall toward the outer surface and thus a fairly rapid drying effect is created. The greater the surface area for evaporation, the faster the drying can occur. A roughcast or pebble-dashed render coating may have three or four times the surface area of a smooth render and can be used in situations where a greater rate of drying is required. Rising dampness in such a wall is not usually as significant a problem if the original lime is maintained (and external ground levels are reduced). Any rising dampness can usually evaporate from the external mortar joints (or render if present) and internally can evaporate from the lime plaster.

Only if the wall is damaged, contains voids or is otherwise defective should moisture pass far into the wall and only in the most extreme of conditions will water penetrate to the inner surface of the wall, perhaps visible to the occupant.

Cement render ‘repairs’

The modern occupant is not willing to accept dampness penetrating the wall during periods of extreme weather, not even if the walls are plastered on the internal surface in a lime-based plaster that will readily and harmlessly dry out as soon as the weather improves.

It is also an easier job for the builder than using a lime render and can be ‘sold’ to the client as a longer lasting application by virtue of its hardness– hardness seemingly being more durable.

Remedies to walls affected by penetrating dampness include render coating and tile hanging, both of which are effective but greatly alter the appearance of the wall. Tile hanging is particularly effective in exposed locations where it has long been a traditional wall covering, protecting the wall from driving rain but allowing the wall to breathe by circulating air freely. In coastal locations this may lessen the damaging effects of the salt that would otherwise be blown onto the walls.

Replacing lime render with cement is very common in the mistaken belief that trying to keep penetrating water out of a wall entirely would be the best approach to relieving or preventing dampness.

Often a cement render will crack. This is sometimes from shrinkage but also commonly caused by movement in the structure of an old building, which, having limited foundations and various other stresses applied to it, continually moves. Both fine and wide render cracks will draw far more moisture into the wall than one might believe possible through the gravity-defying mechanism of capillary action. Rainwater hitting a cement-rendered wall will not be absorbed by the surface, as it would be with a lime render; rather the water will run down the surface of the wall until it reaches a crack. Once drawn behind the render it reaches the brick or stone and soaks in rapidly, saturating anything it can and travelling fast through original lime mortar joints and any voids within the wall structure (very common with stone walls). The cement render prevents any significant evaporation from the outside surface of the wall and moisture builds up until it finds its way to the inner face. The cracked render is liable to further deterioration by differential movement between the ‘flexible’ wall and the inflexible render. The two will want to separate from one another, leading to hollowness behind the render. Water behind the render will freeze in cold weather and the significant expansion of water to its frozen form of ice will further detach the render from the wall (see Photo 1).

In fact the opposite is regularly found to be the case. If applied to damp walls as a remedy for dampness the cement mortar will trap the moisture. Often a wall of any thickness will take up to a year or more to dry out, a length of time and inconvenience unacceptable to many. Water is a very difficult element to control and sealing the outside of the wall with cement render will often encourage the moisture toward the inner surface of the wall, resulting in damp patches to internal plasterwork see Diagram 2 on page 11).

(Continued on page 12)

Photo 1

Page 11 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | © National Energy Services Expansion of salts from within the wall can also easily force paintwork from a painted surface. Timbers within the traditional wall (including lintels, joist ends, window and door frames and wall plates) will absorb moisture from the wall; once wet they will soften, lose compressive and tensile strength and be susceptible to rot and beetle attack. Diagram 1 shows a lime-pointed stone wall performing well. The wall breathes internally as well as externally and the internal lime plastering will absorb and evaporate condensation. Diagram 2 shows a stone wall which has been ‘sealed’ by an external cement render coating and an impervious plaster/paint combination internally. A damp wall will be colder than a dry wall and will therefore be more prone to surface condensation.

Cement pointing ‘repairs’

Diagram 1

Where there is no external render and the masonry is exposed, typically upon re-pointing a traditional brick or stone wall, a hard plug of cement mortar is introduced to the joints on the outer couple of centimetres of the wall. If the building moves, the hard, inflexible new pointing exerts stress on the arises of the bricks or stones to the point where the surface of soft masonry can be broken off. Photo 2 shows brick damage caused at least in part by hard cement pointing. The pointing remains and the ‘fireskin’ (the hard fired outer crust) of the bricks have spalled.

(Continued on page 13)

Diagram 2 Photo 2

Page 12 of 13

SAVA Technical Bulletin Issue 13 | December 2011 | ÂŠ National Energy Services Reporting these deficiencies

(Continued from page 12)

So, how to deal with these matters within the context of the HCS report where we are not giving advice on remedies? When considering a traditional property, if there is no sign of an obvious defect as a result of for example, cement render or cement pointing, do you need to draw the clientâ&#x20AC;&#x2122;s attention to this? Is it in his long term interest to be aware of these sorts of issues? Will it affect his ability to resell the property in years to come? Is there likely to be further deterioration in the elements affected?

Photo 3

This is in contrast to the brickwork in Photo 3, which 3 shows a lime mortar pointed Victorian brick wall. The brick work is in good condition despite these being soft bricks. The wall is dry and the aesthetic appearance good. Note that the vertical joints are slightly narrower than the bed joints. In general, the pointing should be weaker than the masonry it surrounds. Once a brick loses its fireskin the brick will not survive long. Breathability is again also severely restricted by the cement pointing. Where previously water soaked into the wall and evaporated away harmlessly from the lime mortar joint, water is now unable to pass the plug of cement; rather it now has to evaporate through the brick or stone with damage occurring to the masonry.

The answer to these questions is probably yes, but, following the SAVA Condition Rating Protocol for HCS, version 4, there will be many variables that could determine how the report is written. If there is a repair required, then this is easily reported as defective render or pointing. Where the defects have not occurred but a deficient form of repair (using cement in the mortar or render) then to justify your condition rating of 1 you should describe the wall as traditional masonry and point out that a deficient form of repair (using Portland cement) has been carried out and that none of the typical defects associated with this form of repair have yet occurred. SAVA supply fact-sheets on stone walls that could be appended to the report and other fact sheets on masonry (brick and stone) are available from other sources. Mike Ridgell www.horizonsurveyors.co.uk

Send your feedback to bulletins@nesltd.co.uk; back copies of all bulletins and an Index are available in the NES one Useful Documents section. Registration Services: 01908 442 277 registration@nesltd.co.uk Compliance: 01908 442288 compliance@nesltd.co.uk SAVA, The National Energy Centre Davy Avenue, Milton Keynes, MK5 8NA Web: www.nesltd.co.uk

Technical Support Helpdesk: 01908 442105 support@nesltd.co.uk Training enquiries: 01908 442254 training@nesltd.co.uk NES one Credit Top up line: 01908 442299

The content of this technical bulletin is protected by copyright and any unauthorised use, copying, lending or making available of it, howsoever defined, which is not specifically authorised by National Energy Services Ltd., is strictly prohibited. ÂŠ 2011 National Energy Services Page 13 of 13